die4drive help

[0th3r]

Hi!

I'm making Robin's driver; die4drive v1.2.
I have 3 W laser diode. As I rode in the datasheet of irlr MOS it can conduct up to 20A so there is no problem in it. I would like to reach something about 2,5-2,8 Amps.

Will all work if I just repleace the R4, R5 and R8 resistors with ones having more ohms?
In excell file from die4laser.com is something about 5k - 10k to reach 3 Amps. I will of course check the current before conecting the diode.

I'm asking because I don't know if I should also change R9 which is conected from LMH to irlr's gate. Maybe some other parts should be changed? I have bought the small heat sink for MOSFET.

Can somebody help me? All ideas are welcome.
Sorry for my poor english, I'm from Poland

[-bart-]

I'm not aware of V2, I only know V1.1 and V1.2.

I would not change R9 of V1.2 if I were you !

Why don't you contact Robin directly ?

[0th3r]

Sorry for mistake writing v2 I have meant v1.2.

I have written to Robin some time ago on the mail from his site but he didn't answered.

Did someone compared the drifers from forum on the osciloscope?
For example the flexmod p3 and the one with 2 level control on lmh6643 (picture below).
Do this 2 level control really helps with performance?
And connecting laser diode to +5V and the collector of MOS not to the DRAIN and groun, how it changes the behaviour of the driver?

I have all parts to make a die4drive driver, but I will be making the PCB so I can change it a little.

[p1t8ull]

Can't you just change R12 to .1R to increase all drive ranges x10?

The problem you may have is the MOSFET heat transfer is through PCB and only good for a few watts, so you may either need to change the FET for a TO-220 or get the tab of the D-Pak better connected to a heatsink. I used a brass disk and it worked ok -

[0th3r]

Can't you just change R12 to .1R to increase all drive ranges x10?

Hmm it is simply I didn't though about it. I have already ordered 1 Ohm 1% 10W resistor and I would like not to pay more But if it is the best Idea I will do it.
Did you changed your driver this way? (changing R12)

I used a brass disk and it worked ok -

You just made a hole in the PCB and "glued" the brass disc to the back of MOS?

I have 2 x D-PAK so I will use it. Maybe Only the MOSFET can be wired to the PCB and whole MOS would be placed on other brass/copper element. What do you think?

[p1t8ull]

You just made a hole in the PCB and "glued" the brass disc to the back of MOS?

I drilled the PCB and used solder paste to reflow the disk to the FET tab at the same time it was soldered to the PCB.

I have 2 x D-PAK so I will use it. Maybe Only the MOSFET can be wired to the PCB and whole MOS would be placed on other brass/copper element. What do you think?

I'm no EE but I guess that would work if the wires were kept short.

Edit: Just dug out some info from Robin sent over when I was looking at this ages ago -

The Die4Drive is a linear driver rather than switched mode one so if the diode has a Vf of 2V and an operating current of 2.4A the driver will dissipate (5-2)*2.4 = 7.2W (assuming 5V supply)
This is a bit too high for cooling a TO252 (D-Pak) MOSFET through the PCB. Additionally the 1218 / 2512 footprint sense resistor is only good for a watt.

You therefore have 2 options.

1) Retain the 5V supply, swap the 1R sense resistor for a 0.1 R one (all current ranges become x10), remove the D-Pak MOSFET and wire (with short leads) to a TO-220 MOSFET on a reasonable heatsink. (MOSFET must be a low input capacitance, low Vgs-Th, if Cin is too large the 470pF compensation capacitor needs increasing to 1nF.

2) Drop the supply to 3.3V. The input clamping BAV99 needs replacing with a 5.1V SOT-23 Zener (it is the correct pinout to drop straight in, DRV I/P range remains 0 to 5V), Drop the sense resistor to 0.1R (all current ranges become x10), Change the MOSFET (needs to be lower Vgs-Th than the IRLR3105PBF) I have previously used a Vishay SUD40N02-08 with reasonable success (D-Pak, 40A, Vgs-th of 0.6V!)
Driver dissipation with a 3V3 supply and 2.4A 2V Vf diode would be (3.3-2)*2.4 = 3.12W which is OK with through PCB cooling. You could probably push this to 3A if necessary.
Here drive current ranges are x10 but the threshold current adjustment range is (3.3/5)* old threshold adjustment range. If necessary the 22k resistor in series with the Offset POT could be lowered to compensate

[-bart-]

You can also place another 1 Ohm resistor ontop of the other R12. That will give you 0,5 Ohms and will double the current.

Maybe you can ask the admin to change the topic title into "help me designing analog 3A diode driver". You might get more exposure that way.

[0th3r]

I think that I will not bother admin, I have the solution.

The problem is that I have only D-PAK from Holland (In Poland the didn't have MOSFET like this)

What do you think about this solution of heat sink?

The gate and the collector I will wire or juz try to solder D-PAK in position like TO-220.

And I'm wondering about power dissipation, and I think that the biggest part of power which is dissipated, dissipates on the monitor resistor not the MOS. As I read in datasheet of irlr the resistance of conducting MOS is about 0,037 Ohm (Ultra low on-resistance) so even if current is 3A ->
P = R*I^2 = 0,037Ohm * 3A* 3A = 0,333W.
Am I right? It is not much even if cooled by PCB.

But I don't understand this...
U = R/I so Voltage on MOS would be 0,037Ohm/3A = 0,012V
and Voltage on monitoring resistor U=0,1Ohm/3A = 0,0(3) V

In sum it gives not more than 0,05 V...
But whole driver is connected to 5V, so Voltage on the diode is 5V-0,05 = 4,95V. I know that it is not, but where is the mistake in thinking?

It crossed my mind that the ON-resistance (and the smallest) of MOS is 0,037Ohm but the driver doesn't allow it to be so low (gate voltage), and the resistance of MOS is as big as it should be to provide ~2V on diode, and on it own the voltage is ~3V so 3V*3A = 9W. Is that right?

[-bart-]

Simply said :a mosfet is a voltage controlled current source.
To do so, its resitance varies between 0,037 and a few megohms.

Resistance will only be 0,037 if the fet is fully fully on.
NOT in your application.
That figure is only important if you use the fet for switching.

When used as a current source, like in your application, R will vary between 1k and 1 Ohm.

[0th3r]

So everything is clear

I think I will not find irlr TO220 package in my shop but there are some other MOSFETs.

Do you think that SUP60N0618 will do? The parameters are similar.

This is the list of mosfet I can buy, can somebody look with proffesional eye, and help to choose TO220 ?
MOS list.txt